The ability to nodularize cast iron was significantly advanced some 27 years ago when it became known that magnesium, cerium, other rare earths, calcium or their alloys (hereinafter referred to as the alloy) will condition a molten cast iron to form nodular graphite upon solidification. Since that time, the art has moved progressively from (a) adding the alloy to the molten iron charge in the ladle by such methods as plunging, emersion or the sandwich technique, to (b) adding the alloy to the molten charge in a stream immediately before entering the mold, and finally to (c) adding the alloy into a portion of the gating system within the mold.
The earliest use of adding magnesium alloy to a portion of the gating system in the mold was developed particularly with respect to inoculation, a form of gray iron and nodular iron conditioning which not only heralded the way but proved that total nodularization can be carried out within the mold. All of the in-the-mold techniques have possessed one common characteristic, namely: the magnesium alloy has been introduced in a particulate or powdered form. The particulate alloy was (1) introduced in measured scoops poured into a reaction chamber defined in a sand mold, or (2) the alloy was premolded in particulate form within a foam suspension defining the gating system, or (3) a pre-compacted or extruded shape of particulate magnesium alloy was placed in the gating system contacting only one supporting surface. The latter has only been conceptually brought forth; it has not been used in a practical manner to date.
This progression of technology has resulted in a more matched use of magnesium with the needs of the specific casting, it has eliminated fading effects associated with the use of the alloy, eliminated flare and other environmental problems, and aided in reducing costs. Nonetheless, there still remains the likelihood of (a) defects in the casting resulting from undissolved or nonuniformly mixed particulate nodularizing agent which has floated or been carried into the casting cavity, (b) variable segregation of the alloy or a variable solubility rate causing a chemical and metallurgical variation in the casting, (c) unnecessary waste (low yield) resulting from increasing the volume of the gating system to accommodate the particulate matter, (d) the inability to closely target the minimum amount of magnesium alloy to obtain complete or partial nodularization, (e) inclusions in the casting resulting from the greater surface oxidation of the selected nodularizing agent used in particulate form and/or from contaminants in the nodularizing agent and (f) handling problems associated with particulate nodularizing agents.
To achieve increased economy and greater control of the quality of nodularization resulting from introducing the alloy in the mold, some mechanism is needed to overcome the deficiencies above cited which are associated with the particulate form of nodularizing agent.